Symmetrix Virtual Provisioning is a Symmetrix software feature that simplifies storage management and improves capacity utilization. Symmetrix Virtual Provisioning allows storage administrators to create a device that presents an application with more capacity than is physically allocated to it in the storage array.

This article answers the questions about Virtual Provisioning appropriate environments, and implementation considerations.

      Q1: Is virtual provisioning recommended to implement for all Symmetrix equipments?

A1: Symmetrix Virtual Provisioning  is introduced in version 5773 which simplifies storage management and improves capacity utilization. Currently, for VMAX 10K, VP must be implemented without any other choices; For VMAX 20K or 40K, in order to ensure the linear growth of performance with the capacity expansion,  most  SAs still recommend VP being implemented.  If customers worry about oversubscription, they can set the subscription percentage to 100%, or pre-allocate the thin devices. For DMX 3/4, SAs and presales still recommend thick lun to customers.

The implementation considerations are as below:

·         The allocation methods of file systems and databases often allocate space before using it. In addition, many databases pre-allocate space and write zeros to it. This allocated but unused space cannot be shared in a thin pool.

·         Document and media repositories can be a strong fit for Virtual Provisioning. Many organizations will see an opportunity to lower TCO by improving ease of use and capacity utilization for storage associated with test, development, and QA activities.

·         Virtual Provisioning can also help ensure that premium Flash drive resources are highly utilized. Flash drives can offer both unparalleled response times and significant I/Os per GB. Unlike traditional drives, throughput and response time in Flash drives do not steadily decline as utilization of the drive increases.

Q2: Does virtual provisioning mean putting all the disks into a pool whose space will be allocated from?

A2:  Symmetrix Virtual Provisioning introduces a new type of host-accessible device called a “thin” device that can be used in many of the same ways that regular, host-accessible Symmetrix devices have traditionally been used. Unlike regular Symmetrix devices, thin devices do not need to have physical storage completely allocated at the time the devices are created and presented to a host. The physical storage that is used to supply drive space for a thin device comes from a shared “thin storage pool” that has been associated with the thin device. A thin storage pool is comprised of a new type of internal Symmetrix device called a “data device” that is dedicated to the purpose of providing the actual physical storage used by thin devices. When they are first created, thin devices are not associated with any particular thin pool. An operation referred to as “binding” must be performed to associate a thin device with a thin pool.

A thin pool must satisfy all of the following requirements:

·         Only data devices may be placed in a thin pool.

·         All data devices in the thin pool must be of the same emulation type.

·         All data devices in the thin pool must be of the same protection type.

·         Data devices in the pool should all reside on drives that have the same rotational speed. Fully Automated Storage Tiering with Virtual Pools (FAST VP) enforces this recommendation if the pool is added to a FAST VP tier.

·         Data devices in the pool should generally be spread across as many DAs and drives of a given speed as possible.

·         Data devices should be evenly spread across the DAs and drives. The wide striping provided by Virtual Provisioning will spread thin devices evenly across the data devices. The storage administrator must ensure that the data devices are evenly spread across the back end.

·         All data devices in the thin pool should be of the same size. Using different size devices could result in uneven data distribution.

·         Data device sizes should be as large as possible to minimize the number of devices required to encompass the desired overall pool capacity.

·         Each drive must be divided into at minimum eight hypers in order to maintain adequate disk queue depth.

Q3: In what environment is Virtual Provisioning being recommended to implement?

A3:  Organizations using Virtual Provisioning should have well-understood application capacity growth requirements in order to avoid unexpected consumption of pool capacity. Organizations can improve ease of use in these environments. Data layout becomes simpler as automated wide striping provides equivalent or potentially better performance, with less planning and labor than is required with standard provisioning.

Besides, Virtual Provisioning is appropriate for applications for which some performance variability can be tolerated. Some workloads will see performance improvements from wide striping with Virtual Provisioning, however, when multiple thin devices contend for shared spindle resources in a given pool, and when pool utilization reaches higher levels, the performance for a given application and thin device might become more variable.

                                                                                                                                              

Author: Jiawen Zhang